Cobalt(III) diazabutadiene precursors for metal deposition: Nanoparticle and thin film growth

Article abstract of DOI:10.1021/ic402317g

We report the synthesis and characterization of a family of cobalt(III) metal precursors, based around cyclopentadienyl and diazabutadiene ligands. The molecular structure of the complexes cyclopentadienyl-Cobalt(III)(N,N′- dicyclohexyl-diazabutadiene) (2c) and cyclopentadienyl-Cobalt(III)(N,N′- dimesityl-diazabutadiene) (2d) are described, as determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl derivative CpCo(ⁱPr₂-dab) (2a) as a possible cobalt metal chemical vapor deposition (CVD) precursor. Atmospheric pressure CVD (AP-CVD) was employed using precursor 2a to synthesize thin films of metallic cobalt on silicon substrates under an atmosphere of hydrogen (H₂). Analysis of the thin films deposited at substrate temperatures of 250 C, 275 C, 300 C, 325 C, and 350 C, respectively, by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal temperature dependent growth features: films grown at 325 and 350 C are continuous and pinhole free, whereas those films grown at substrate temperatures of 250 C, 275 C, and 300 C consist of crystalline nanoparticles. Powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic cobalt. Raman spectroscopy has also been used to prove the absence of cobalt silicides at the substrate/thin film interface.

Full text of DOI:10.1021/ic402317g

Article
pubs.acs.org/IC
Cobalt(III) Diazabutadiene Precursors for Metal Deposition:
Nanoparticle and Thin Film Growth
Thomas Pugh,† Samuel D. Cosham,† Jeff A. Hamilton,† Andrew J. Kingsley,‡ and Andrew L. Johnson*,†
†Department of Chemistry, University of Bath, Bath, BA2 7AY, United Kingdom
‡SAFC-Hitech, Power Road, Bromborough, Wirral, CH62 3QF, United Kingdom
S
* Supporting Information
ABSTRACT: We report the synthesis and characterization of a family of cobalt(III) metal precursors, based around
cyclopentadienyl and diazabutadiene ligands. The molecular structure of the complexes cyclopentadienyl-Cobalt(III)(N,N′-
dicyclohexyl-diazabutadiene) (2c) and cyclopentadienyl-Cobalt(III)(N,N′-dimesityl-diazabutadiene) (2d) are described, as
determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted the isopropyl
derivative CpCo(iPr2-dab) (2a) as a possible cobalt metal chemical vapor deposition (CVD) precursor. Atmospheric pressure
CVD (AP-CVD) was employed using precursor 2a to synthesize thin films of metallic cobalt on silicon substrates under an
atmosphere of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 250 °C, 275 °C, 300 °C, 325 °C,
and 350 °C, respectively, by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal temperature
dependent growth features: films grown at 325 and 350 °C are continuous and pinhole free, whereas those films grown at
substrate temperatures of 250 °C, 275 °C, and 300 °C consist of crystalline nanoparticles. Powder X-ray diffraction (PXRD) and
X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic cobalt. Raman spectroscopy has also been
used to prove the absence of cobalt silicides at the substrate/thin film interface.
especially porous cobalt films have been found to be active
materials for the evolution of oxygen and hydrogen in alkaline
solutions.8 Thin films of cobalt and cobalt oxide have also
found utility as components of energy storage devices, for
example, LiCoO2 in lithium ion batteries.9 Resultantly cobalt
thin films have been deposited by various means including
electrodeposition,10 sputtering,11 electron beam evaporation,12
chemical vapor deposition (CVD),6c,13 and more recently
atomic layer deposition (ALD).
Research has demonstrated that CVD is capable of
depositing thin cobalt films of higher quality than sputtering
methods. However, despite the advantages of increased thin
film purity and uniformity there are limited reports of cobalt
CVD, and more specifically, the development of novel chemical
INTRODUCTION
■
Metal thin films and nanostructures are in demand for a range
of technological applications, finding use as active materials in
microelectronics, sensors, and catalysts, as well as reflective and
refractive coatings for optical devices, and as decorative and/or
protective coatings.1 Thin films of cobalt, cobalt oxide, cobalt
alloys, and cobalt/X multilayers (where X is a nonmagnetic or
insulating material) have all been the subject of renewed
interest over the past decade because of their relevance to
magnetic devices utilizing phenomena such as giant magneto-
resistance (GMR)2 and tunneling magnetoresistance (TMR),3
since cobalt exhibits the highest magnetic anisotropy of any
transition metal.4 A major motivation for cobalt film growth has
been the formation of CoSi2,5 which can act as both metallic
interconnections and ohmic contacts in silicon based devices, as
well as Schottky contacts in the field of optoelectronics,6 and as
metal caps for copper interconnects.7 More recently, cobalt and
Received: September 12, 2013
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Chart 1. Co Metal CVD and ALD Precursors Reported in the Scientific Literature to-Date
Table 1. Diazabutadiene Ligands Used in This Study
precursors. To date, the literature has only highlighted a limited
number of cobalt CVD precursors which include Co2(CO)8
(I),6e,11c,13d,k,m Co(NO)(CO)3 (II),6a,13e,k,14 CoCF3(CO)4
(III),13d CpCo(CO)2 (IV),6d−h,13c,d CoH(CO)3 (V),15 CoH-
[nPrOP(OMe)2]3 (VI),16 Cp2Co (VII),13d Co(acac)2/3
(VIII),13i,l,17 Co2(CO)6(μ2-C2(H)tBu) (IX),13h and Co(Allyl)-
(CO)3 (X)18 (Chart 1).
The paucity of chemical literature concerning the production
of cobalt thin films is largely due to the limited number of
precursors displaying both volatility and thermal stability. For
example, as solids at operation temperature, Co2(CO)8 (I),
Cp2Co (VII), and Co(acac)2 (VIII) all suffer from variable
vapor pressures, caused by changing precursor surface area
during processing, which results in unreliable thickness control
and the possibility of film contamination from the shedding of
particles.13d,l In contrast Co(CO)3(NO) (II), which is a liquid
with a high vapor pressure, is susceptible to the incorporation
of carbon, oxygen, and nitrogen impurities associated with
ligand decomposition, requiring exceedingly stringent con-
ditions to avoid contamination of the thin films deposite-
d.6a,13e,k,14
The liquid precursor material CpCo(CO)2 (IV) is a volatile
(0.5 Torr at 25 °C) precursor which has been widely
investigated as a CVD precursor to both cobalt metal and
cobalt silicide. While the literature has shown atmospheric
pressure-CVD (AP-CVD) of (IV) in a H2 atmosphere to yield
high purity cobalt films (99%) at rates of up to 60 Å/min, low
pressure-CVD (LP-CVD) of (IV) invariably leads to films
heavily contaminated with carbon.13c In addition, the precursor
needs to be stored at low temperatures to prevent
decomposition during storage, a problem common to the
entire range of carbon monoxide containing precursors (I−V,
IX, and X).
precursor development has not advanced at an equal pace, with
precursors such as Co2(CO)8 (I),19 CpCo(CO)2 (IV),20
Cp2Co (VII),20,21 and Co(Allyl)(CO)3 (X),22 originally
developed for CVD, featuring as precursors for ALD of cobalt
metal. Only very recently has there been resurgence in the
development of new cobalt metal precursors, with the
publication of the synthesis of stable and highly volatile
complexes of cobalt such as the bis-amidinate complex (XI)20,23
and bis-diazadienyl (XII)24 complexes alongside their applica-
tion in the ALD of thin films of cobalt metal and cobalt oxide.25
The general lack of suitable precursors for cobalt deposition
highlights a need for the design and development of novel
precursors which amalgamate desirable properties such as
thermal stability and high volatility and are capable of
depositing highly pure films at low deposition temperatures.
Herein, we report the synthesis, thermogravimetric analysis
(TGA), and AP-CVD of a series of organometallic Co(III)
precursors containing N,N′-dialkyldiazabutadiene and N,N′-
diaryldiazabutadiene, (R2-dab) ligands 1a−e, (Table 1) of the
general form (η5-C5H5)Co(R2-dab). It should be made clear
here, that several of the complexes reported ibid. (2a, 2b and
2e) have been synthesized previously by Dieck et al. using
alternative routes,26 but these complexes have never before
been investigated for their volatility and potential utility in the
deposition of cobalt metal thin films, while molecular structures
of the complexes 2c and 2d are reported here for the first time.
Diazabutadiene (or α-diimine) ligands have attracted
significant interest because of their ability to stabilize metal
centers in formally low oxidation states, a direct consequence of
the presence of a low lying ligand-based π* orbital, capable of
accepting electron density from the metal containing frag-
ment.26 This orbital can also be occupied through metal-to-
ligand charge transfer (MLCT), through facile, and reversible,
chemical or electrochemical reduction or through direct ground
state metal-to-ligand two-electron transfer. As a consequence of
their noninnocent redox behavior these ligands, when attached
While recent focus has been directed toward lower
temperature growth methods, such as ALD and plasma
assisted-ALD, to avoid dewetting and nanoparticle growth,
B
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
to a metal center have been shown to exist in one of four
distinct forms each with distinguishing structural features
(Chart 2): (i) a dative coordination of the nitrogen atoms to
Molecular Structures of 2c and 2d. Of the five
complexes reported in this study, single crystals suitable for
single crystal X-ray diffraction of only two complexes, 2c and
2d, could be isolated; these were grown from saturated hexane
solutions at −28 °C and were structurally characterized by
single crystal X-ray diffraction to unambiguously determine the
solid state molecular structures of the products. Experimental
crystallographic data are summarized in Table 2, selected bond
lengths and angles for 2c and 2d are shown in Table 3, and the
molecular structures of the complexes are shown in Figure 1.
Chart 2. Possible Forms of the Metal Diazabutadiene
Systems
the metal atom (form A) with short carbon−nitrogen bonds,
long carbon−carbon and metal−nitrogen bonds, (ii) a dative
coordination of the nitrogen atoms to the metal atom with
associated back bonding from the metal into the π* orbital of
the ligand (form B) with intermediate carbon−carbon and
carbon−nitrogen bonds and short metal−nitrogen bonds, (iii)
a single electron reduced delocalized diazabutadiene anion
coordination to the metal, with intermediate carbon−carbon
and carbon−nitrogen bonds and long metal−nitrogen bonds
(form C), and (iv) a two-electron reduced diamide ligand, with
short metal−nitrogen and carbon−carbon bonds and long
carbon−nitrogen bonds (D).
Table 2. Crystallographic Data for the Complexes 2c, and 2d
2c
2d
empirical formula
formula weight
T/K
C19H29CoN2
344.37
C25H29CoN2
416.43
150(2)
150(2)
crystal system
space group
a (Å)
triclinic
monoclinic
P21/a
P1
̅
8.4720(10)
10.4340(10)
10.952(2)
105.676(4)
107.831(4)
96.116(9)
868.2(2)
2
7.8580(4)
31.7460(18)
9.0620(4)
b (Å)
c (Å)
α (deg)
While an examination of the literature shows that the η2-R2-
dab coordination mode is the most prevalent,27 R2-dab ligands
can also bind to metal centers in an η4-{N2C2} coordination
mode to form π-complexes with metals.28
β (deg)
112.482(3)
γ (deg)
V
2088.80(18)
Z
4
ρcalc mg/m−3
μ(Mo−Kα), mm−1
F(000)
1.317
1.324
RESULTS AND DISCUSSION
0.987
0.834
■
1.040
880
Synthesis. Complexes 2a−e were prepared by the reaction
of ClCo(PPh3)3 with NaCp, followed by a thermally driven
substitution of PPh3 with the appropriate N,N′-dialkyldiazabu-
tadiene (Scheme 1). Complex 2a was isolated as a dark brown
crystal size, mm
θ range (deg)
reflections collected
0.40 × 0.20 × 0.05
2.68 to 25.00
14683
0.20 × 0.17 × 0.05
2.75 to 27.50
19648
independent reflections
[R(int)]
3043
[R(int) = 0.0447]
4606
[R(int) = 0.1655]
Scheme 1. Outline of the Synthetic Methodology Used in the
Production of Complexes 2a−e
max.,min transmission
0.8501 and 0.8270
1.040
0.9595 and 0.8509
1.018
goodness-of-fit
final R1 (wR2) [I > 2σ(I)] R1 = 0.0291, wR2 =
R1 = 0.0754, wR2 =
0.0861
0.0670
final R1 (wR2) (all data)
R1 = 0.0333, wR2 =
0.0693
R1 = 0.2204, wR2 =
0.1206
largest diff. peak and hole, 0.280 and −0.539
0.454 and −0.535
e Å−3
oil and purified by distillation (5 × 10−2 mbar, 100 °C),
complexes 2b and 2c were isolated as dark brown solids
purified by sublimation (5 × 10−2 mbar, 100 °C) and
complexes 2d and 2e were isolated by recrystallization from
saturated hexane solutions at −28 °C.
In the solid state complexes 2c and 2d adopt mononuclear
structures, in which the metal centers possess a pseudo-trigonal
planar environment, comparable to the related iridium-dab
complex [Cp*Ir(R2dab)] (R = 2,6-dimethylphenyl),29 the
diaryltetraazadiene complexes [CpCo(Arf2N4)] (Arf = C6F5)
1
Room temperature H NMR of complexes 2a−e showed all
of the complexes to be diamagnetic,26 and to possess
characteristic singlet resonances for η5-Cp-H between δ = 4.1
and 4.8 ppm; R2-dab backbone protons (CH) showed singlet
resonances in the range of δ = 6.6−7.2 ppm. 1H NMR
resonances for the alkyl and aryl substituents attached to the
coordinated R2-dab ligands were also present. Upon coordina-
tion of the R2-dab ligands to the cobalt atom there is a notable
change in the chemical shift for both CH groups, and N-alkyl or
N-aryl substituents, for example, N,N′-di-isopropyl-diazabuta-
diene backbone CH-resonances for uncoordinated (1a) and
coordinated (2a) are δ = 7.9 ppm and 7.0 ppm respectively;
correspondingly the methine CH of the isopropyl substituent
changes from δ = 3.5 ppm to δ = 4.9 ppm upon coordination to
the cobalt.
Table 3. Selected Bond Lengths and Angles for 2c and 2d
2c
Bond Distances (Å)
1.677
2d
Co-(η5-C5H5)(cent)
1.695
Co−N(1)/Co−N(2)
1.887(2)/1.859(2)
1.855(4)/
1.844(6)
NC
C−C
1.336(5)/1.332(5)
1.339(7)/
1.343(7)
1.382(3)
1.383(6)
Bond Angles (deg)
N(1)−Co−N(2)
82.99(7)
82.91(17)
Co−N(1)C/Co−N(2)C
113.45(12)/
114.78(13)
115.0(3)/
115.3(3)
C
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. Diagram showing the molecular structures of the complexes 2c (A) and 2d (B) (50% probability ellipsoids). Hydrogen atoms have been
omitted for clarity.
Table 4. Co−N, N−C, and C−C Bond Distances in Selected Cobalt-dab Complexes
a
complexes
oxidation state/dn
Co−N
N−C
C−C
ref
[(tBu2-dab)CoCl2]
[(Dipp2-dab)CoBr2]
[(Ph2-dab-Me2)CoCl2]
[(Xyl2-dab-Me2)CoBr2]
[(Mes2-dab-Me2)CoCl2]
[(Dipp2-dab-Me2)CoCl2]
[(Dipp2-dab-Me2)CoI2]
[{tBu2-dab}2Co]
2+/ d7
2+/ d7
2+/ d7
2+/ d7
2+/ d7
2+/ d7
2+/ d7
2+/ d7
2+/ d7
−1/d10
−1/d10
3+/d6
2.07
2.05
2.04
2.05
2.05
2.04
2.05
1.93
1.93
1.96
1.96
1.87
1.85
1.26
1.34
1.28
1.28
1.28
1.29
1.28
1.34
1.35
1.27
1.30
1.34
1.34
1.37
1.51
1.53
1.50
1.52
1.53
1.50
1.53
1.40
1.41
1.44
1.43
1.38
1.38
1.33
33
34
35
36
35
35
37
24
38
39
39
[{(C6F5)2-dab-Me2}2Co]
[(iPr2-dab)Co(NO)(CO)]
[(Dipp2-dab)Co(NO)(CO)]
2c
this work
this work
29
2d
3+/d6
[Cp*Ir(Xyl2-dab)]
3+/d6
a
Mes =2,4,6-trimethylphenyl; Dipp =2,6-diisopropylphenyl; Xyl =2,6-dimethylphenyl; R2-dab-Me2 = R-NC(Me)-C(Me)N-R; Cp* = (η5-
C5Me5).
and [CpNi(Ar2N4)] (Ar = C6H4Me)30 and [Cp*Co(Bipy)],31
all of which share a common structural form based on the
similarities of the nitrogen containing ligand systems. In both
2c and 2d the {CoN2C2} rings are planar (the mean deviation
of an atom in the ring from the least-squares plane of the ring
being 0.0007 Å and 0.0051 Å respectively) and the Cp ligands
are essentially orthogonal to the {CoN2C2} plane (2c: 89.60°,
2d: 89.85°).
Co-R2-dab systems and are much more comparable to Co−N
single bonds found in cobalt-amide complexes,32 in which Co−
N secondary interactions (multiple bond character) are invoked
(cf. CoN: 1.66−1.68). The precise oxidation state of the
ligands, and consequently of the metal centers in dab-
complexes have previously been assigned, by others, on the
basis of a comparison of the M−N, N−C, and C−C bond
lengths within complexes, in which the ligands are either
neutral (dab), radical monanions ([dab]•−) or dianionic ligands
([dab]2−). A comparison of the Co−N, N−C and C−C bond
The average Co−N bond lengths of about 1.870 Å are
relatively short compared to other structurally characterized
D
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
lengths of the R2-dab ligands in complexes 2c and 2d with
related Co-dab containing complexes is shown in Table 4.
A comparison of the bond parameters in Table 4 suggest that
the complexes fall into several distinct classes with respect to
the oxidation state of the dab ligands, and hence the Co atom.
The simple Co dihalide complexes, for example, [(tBu2-
dab)CoCl2], display a distribution of bond lengths which
have previously been ascribed to α-diimine coordination
complexes in which the neutral diimine ligand possess
alternating long Co−N; short N−C; long C−C, bonds
representative of single/double/single bond character (form
A, Chart 2). In contrast, the bis-dab cobalt complex, [{tBu2-
dab}2Co] and [{(C6F5)2-dab-Me2}2Co], which have been
unequivocally described as Co(II) complexes containing two
radical monoanionic [dab]•− ligands, clearly show a length-
ening of the N−C bonds and a concomitant shortening of the
Co−N/C−C bonds, indicative of a single electron delocalized
about the π-orbitals of the dab ligand (form C, Chart 2). Both
of these types of system are ascribed a Co(II) oxidation state
(d7 electronic configuration); an observation that is confirmed
by the paramagnetic nature of the complexes and density
functional theory (DFT) calculations, and in the case of [{tBu2-
dab}2Co] and [{(C6F5)2-dab-Me2}2Co] by SQUID measure-
ments and electron spin resonance (ESR) spectroscopy which
are consistent with a divalent Co d7 ion and a pair of radical
monoanionic ligands.
Figure 2. Diagram showing the distortion away from linearity of the
Co-Cp(cent) vector in 2c.
2a−e were performed to gain insight into relative volatilities
and thermal stabilities (Figure 3).
The Co complexes, [(iPr2-dab)Co(NO)(CO)] and [(Dipp2-
dab)Co(NO)(CO)], reported by Kaim et al. display, what are
ascribed as bond lengths which are intermediate between the α-
diimine complexes and the cobalt(II) diimine diradical
complexes.39 These diamagnetic complexes are recognized by
Kaim et al. as formally Co(-I) species with nonreduced dab
ligands and a d10-configured metal atom. Bond length
distortions away from the long/short/long pattern expected
in simple α-diimine complexes is effected by π-back bonding
from the metal center into the π* orbital of the diimine ligand
(form B, Chart 2).
An examination of the Co−N/N−C/C−C bond lengths in
complexes 2c and 2d suggest a different bonding model to
those previously discussed; as noted earlier in comparison to
the related systems shown in Table 4 the Co−N bonds in 2c/d
are short, with the C−N/C−C bond lengths in strong
agreement with what would be expected for a doubly reduced
[dab]2− ligand with single N−C and double C−C bonds (form
D, Chart 2). Complexes 2c/d are both unequivocally 18-
electron diamagnetic complexes, with computational studies
suggesting a closed shell d6-electronic configuration and a
formal Co(III) oxidation state,26,29 which is in agreement with
the related iridium complex [Cp*Ir(R2dab)] (R = 2,6-
dimethylphenyl).29
Figure 3. TGA traces of 2a−e from 30 to 400 °C. Experiments were
run under N2 (50 mL/min) at a ramp rate of 20 °C/min.
These analyses were carried out with an instrument that was
housed in a nitrogen filled purge-box to minimize reaction with
atmospheric moisture/air. Compounds 2a−e were found to
undergo mass loss to yield stable residues of between 1.5 and
6.3%, over the temperature range 190−280 °C, which are lower
than the expected values for cobalt metal from each respective
complex (Table 5) indicating a significant degree of
Table 5. Expected % Residue, % of Non-Volatile Residue and
Onset Temperature of Volatilization/Decomposition for
2a−e
onset
a
precursor expected % for Co % nonvolatile residue (temp.)
temp.
2a
2b
2c
2d
2e
22.3%
20.2%
17.1%
14.2%
11.8%
1.5% (190 °C)
4.6% (215 °C)
4.3% (280 °C)
3.6% (275 °C)
6.3% (255 °C)
98 °C
89 °C
95 °C
183 °C
171 °C
a
The temperature at which 1% mass loss has occurred.
In the solid state the cyclohexyl substituents in 2c are both
arranged in a chair conformation but with one cyclohexyl group
orientated toward the {Cp} ligand and the other directed away
from the {Cp} ligand; resultantly the centroid of the {Cp}
ligand deviates from the nominal C2 axis of the complex by
2.94° (Figure 2), presumably to reduce steric strain in the solid
state. In comparison 2d, in which the mesityl substituents (viz.
their planes) are orientated roughly orthogonal to {CoN2C2}
plane [N(1)−C(12)−C(17): 73.56°, N(2)−C(22)−C(27):
82.89°], experience no similar distortion in the solid state.
Thermal Profile of Complexes and Use as Deposition
Precursors. Thermogravimetric analyses (TGA) of complexes
volatilization in all cases. Complexes 2b and 2c appear to
have multistep decomposition pathways, as indicated by the
changing gradient of the TGA curve, a feature which is much
more pronounced for the cyclohexyl-derivative 2c. In contrast
2a, 2d, and 2e all have TGA curves which present as a relatively
sharp single step weight loss that combine a degree of both
volatilization and decomposition. Of the complexes investigated
complex 2a, which is a liquid at room temperature, shows the
highest degree of volatility losing approximately 98.5% of its
E
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
original mass between 98 and 190 °C, suggesting a high degree
of thermal stability.
densities, the average size of the aggregates is larger in the latter
(154 nm vs 238 nm), which is likely to be a result of faster
growth rates at higher deposition temperatures. The nucleation
density of films grown at 275 °C was found to be lower, but the
aggregate sizes of the nanoclusters are larger (375 nm).
The nanoparticles grown from complex 2a at temperatures of
300 °C and below exhibit a surprising size regularity within
each sample (see Figure 4). More significantly, particle size
appears to be related to the deposition temperature, and further
studies on controlling the size of cobalt nanoparticles are
currently underway.
Films grown at substrate temperatures of 325 and 350 °C are
seen to be continuous by SEM indicating rapid nucleation and
thin film growth (Figure 5) on silicon. Films grown at 325 °C
consist of larger particles, which display excellent surface
coverage, whereas films grown at 350 °C consist of cylindrical
nanorods which protrude from the surface of the substrate.
Cross-sectional SEM imaging (Figure 5) show both films to be
continuous, and have excellent thickness uniformity; the
thicknesses of films grown at 325 and 350 °C were measured
to be 112 and 254 nm, translating to a growth rate of 3.73 nm/
min and 8.47 nm/min, respectively, which compares favorably
to previously reported cobalt metal deposition precursors.
Analysis of the films by atomic force microscopy (AFM)
(Figure 6) reveals that films deposited at higher temperatures
(350 °C) to be rougher than those grown at 325 °C (Rms = 98
nm (325 °C) and 0.13 μm (350 °C)).
Combined with its liquid nature at room temperature and
high degree of volatilization complex 2a was deemed a suitable
candidate for assessment as a Co deposition precursor.
Cobalt Deposition and Thin Film Analysis. Cobalt was
deposited onto silicon (400) wafers using the complex 2a at
atmospheric pressure with a cold-walled Electrogas CVD
apparatus. The deposition of cobalt metal was investigated at
five different substrate temperatures; 250 °C, 275 °C, 300 °C,
325 °C, and 350 °C, respectively. In all of the deposition runs
the precursor and the carrier gas lines were externally heated to
130 °C, and the pressure during deposition was maintained at
760 Torr. H2 gas was used as the carrier gas at a flow rate of 0.3
L min−1. Table 6 shows the general physical parameters used
throughout the deposition experiments.
Table 6. General Physical Parameters for the Atmospheric
Pressure CVD (AP-CVD) of Complex 2a
CVD parameters
substrate temperature (°C)
operating pressure (Torr)
carrier gas
250
760
H2
275
760
H2
300
760
H2
325
760
H2
350
760
H2
carrier flow rate (L min−1
bubbler flow rate (L min−1
)
0.7
0.7
0.7
0.7
0.7
)
0.3
0.3
0.3
0.3
0.3
temp of Co-precursor bubbler and
carrier gas lines (°C)
130
130
130
130
130
To ascertain the elemental composition of the thin films,
analysis by high resolution X-ray photoelectron spectroscopy
(XPS) was performed; however, XPS data for films deposited
from complex 2a at 300 °C are not reported because of the
inability to obtain reliable measurements as a consequence of
the significantly reduced surface coverage and larger particle
size. In general, analysis of the as-deposited films revealed the
presence of significant peaks associated with carbon (1s = 284
eV) and oxygen (1s = 532 eV). Following an argon etch, peaks
associated with metallic cobalt (2s = 926 eV, 2p3/2 = 779 eV,
LMM = 716 eV, 3s = 101 eV and 3p = 60 eV) increased in
intensity and peaks associated with carbon and oxygen reduced
significantly. Figure 7 shows a typical example of a cobalt XPS
spectrum (deposited at 350 °C) showing the presence of
photoelectron peaks associated with metallic cobalt [Co2p
deposition duration (mins)
30
30
30
30
30
Films deposited at temperatures of 300 °C and below
appeared powdery, silvery-blue in color and discontinuous to
the naked eye, whereas films deposited at 325 and 350 °C
appeared metallic and continuous, with some brown discolor-
ation in the latter; scanning electron microscopy (SEM)
micrographs of the deposited films are shown in Figures 4 and
5. SEM analysis showed films deposited at a substrate
temperature of 300 °C and below to be discontinuous and
consist of aggregations of nanoparticulate material, suggesting
that initial nucleation on silicon is followed by preferential
growth on cobalt.40 Comparing films deposited at substrate
temperatures of 250 and 300 °C, which have similar nucleation
Figure 4. SEM micrographs for films deposited onto Si at 250 °C (left), 275 °C (middle), and 300 °C (right) using complex 2a.
F
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 5. SEM micrographs of films deposited onto Si at 325 °C (top) and 350 °C (bottom) using complex 2a.
consequence of ex-situ oxidation of the deposited cobalt films,
with the more porous nature of films deposited at 350 °C
leading to greater penetration of oxygen and an increase in
oxidation. Similarly carbon content in the films is attributed to
contamination by atmospheric carbon containing materials
post-deposition which can be embedded into films following
argon etching.
It is worth noting however, previous reports of cobalt
deposition onto silicon substrates, using MOCVD precursors,
have been accompanied by the concomitant formation of cobalt
silicide materials (i.e., Co2Si, CoSi, and CoSi2),13e,k,41 although
it should also be noted that Co-silicide production is typically a
two stage process which involves the deposition of pure Co on
Si, typically by physical vapor deposition (PVD) means. This
step is followed, in a second stage, by a thermally driven solid
state reaction with the Si substrate to grow CoSi2 (>500
°C).6a,42 In the case of films deposited between 250 to 350 °C
there is no evidence from XPS analysis of the formation of
Co2Si, CoSi, or CoSi2, all of which are readily identifiable.42d
Raman spectroscopy, a technique which is sensitive to the
presence of both CoSi and Co2Si, but not CoSi2 and Co phases,
was used to further interrogate the nature of the thin-films.
While an intense Raman band at 520.9 cm−1 revealed the
presence of the underlying silicon substrate, no Raman bands
attributable to CoSi or Co2Si were observed.43
Powder X-ray diffraction (PXRD) analysis (Figure 8)
revealed crystal growth in all films deposited using 2a to be
highly selective, showing one intense reflection at 2θ = 44.3°
(highlighted in blue, Figure 8), which corresponds to the (111)
Miller plane associated with face centered cubic (fcc) cobalt
metal;44 all other reflections are associated with the (400)
silicon substrate. Increasing the substrate temperature results in
an intensification of the (111) reflection, which is associated
with an increasing film thickness, increasing film coverage and a
higher rate of surface diffusion associated with higher
temperature deposition, leading to an increase in the crystallite
size. In the case of all films examined by PXRD, peaks
attributable to Co2Si ([031] 2θ = 45.27°)45 CoSi ([210] 2θ =
45.67°; [211] 2θ = 50.32°)46 and CoSi2 ([220] 2θ = 47.91°)47
were absent from the spectra.
Figure 6. AFM images of the thin film deposited at 325 °C (A) and
350 °C (B) respectively.
region: 793.24 eV (Co 2p1/2); 778.04 eV (Co 2p3/2)] and the
1s regions for carbon and oxygen, which are common
contaminants in deposited cobalt films.
Analysis indicates that films deposited at a substrate
temperatures between 250 and 300 °C show a relatively high
silicon content; not inconsistent with deposition onto silicon
and formation of nanoparticles. In fact in all cases, discounting
background silicon values from our calculations suggests that
moderately high purity thin films of cobalt have been formed
(94.3%, 87.9%, 93.2%, and 90.3% at.% of Co respectively), with
unquantifiable traces of carbon and trace amounts of oxygen
(Table 7). As the substrate temperature increases to 325 and
350 °C the degree of oxygen contamination increases to 6.17
at.% and 7.52 at.%, respectively, however, carbon contami-
nation remains at low levels. Because of the absence of oxygen
within the precursor, oxygen contamination is thought to be a
G
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 7. Survey XPS spectrum of a typical film deposited at a substrate temperature of 350 °C (above), with the Co2p region [793.24 eV (Co
2p1/2); 778.04 eV (Co 2p3/2)] highlighted (inset), and the 1s regions for oxygen (bottom left) and carbon (bottom right).
Table 7. Atomic % of Elements in Cobalt Thin Films
Deposited at between 250 and 350 °C Post-Ar Etching (15
s)
substrate temperature
at.% Co
at.% O
at.% C
at.% Si
a
250 °C
275 °C
325 °C
350 °C
35.75
11.10
84.40
80.13
2.15
1.53
6.17
7.52
trace
trace
trace
1.08
62.10
87.37
9.43
a
a
a
11.27
a
Quantification was performed assuming zero oxygen contribution
from the silicon substrate. Values are expressed as atomic percentages.
Resistivity measurements were conducted using a four point
probe on the two films deposited using complex 2a at substrate
temperatures of 325 and 350 °C (Table 8) which were shown
by SEM analysis to be continuous; no measurements were
conducted on samples deposited at lower deposition temper-
atures as the films were discontinuous. The average bulk
resistivity values for films deposited at 350 and 325 °C were
calculated to be 179.6 μΩ cm and 18.6 μΩ cm, the lower of
which approaches the value for bulk cobalt (5.6 μΩ cm).13e
The higher purity and continuity of films deposited at the lower
Figure 8. XRD patterns for an uncoated (400) silicon substrate and
films deposited between 250 and 350 °C. Highlighted line shows the
Co (111) Miller plane.
deposition temperature of 325 °C results in a lower resistivity
value for the film, which is in agreement with previously
reported data.13m
H
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
g, 2 mmol) was then added, and the reaction mixture was refluxed for a
period of 0.5 h, during which time a color change from deep red to
brown was observed. The THF was removed in vacuo and the
remaining material was extracted into hexane (3 × 20 mL); the
combined extracts were filtered through Celite, the solvent was
removed in vacuo, and the oily residue was distilled (5 × 10−2 mbar,
100 °C) yielding 0. 91 g (74%) of a yellow-brown liquid. Analysis.
Calc.: C 59.09%, H 8.01%, N 10.60%; Found: C 58.93%, H 7.89%, N
Table 8. Average Bulk Resistivity (ρ) and Sheet Resistance
(RS) Values for Continuous Cobalt Films Deposited at 325
and 350 °C Respectively Using Complex 2a
a
thickness (nm)
[growth rate (nm/min)]
RS (Ω/
□)
ρ (μΩ
temperature
cm)
325
350
112 [3.73]
254 [8.47]
1.66
7.07
18.6
179.6
1
i
10.54%. H NMR (300.22 MHz, C6D6, 298 K) δ: 1.49 (d, 12H, Pr-
Me, J = 6.67 Hz), 4.56 (s, 5H, η5-Cp), 4.93 (sep, 2H, iPr-CH, J = 6.67
Hz), 6.96 (s, 2H, HCN). 13C{1H} NMR (75.50 MHz, C6D6, 298 K)
δ: 24.6 (iPr-Me), 64.2 (iPr-CH), 75.8 (η5-Cp), 133.8 (HCN).
Complexes 2b−e were synthesized in an analogous manner to that
of system 2a with the exception of the addition of N,N′-di-tert-
butyldiazabutadiene, 1b, (0.84 g, 5 mmol) N,N′-dicyclohexylbutyl-
diazabutadiene, 1c, (1.10 g, 5 mmol), N,N′-dimesityldiazabutadiene,
1d, (1.46g, 5 mmol), and N,N′-2,6-di-isopropylphenyldiazabutadiene,
1e, (1.88 g, 5 mmol) respectively.
a
The bulk resistivity of Cobalt = 5.6 μΩ cm (at 0 °C).
CONCLUSIONS
■
This paper reports the synthesis and thermal analysis of five
CpCo(R2-dab) complexes and reports the first study of their
use as metal deposition precursors. Because of its high thermal
stability and physical properties, compound 2a was identified as
a potential candidate for deposition studies. Thin films were
deposited onto Si substrates in the temperature range of 250−
350 °C under an atmospheric pressure of H2. Films deposited
at all temperatures were found to have low carbon
contamination by XPS analysis, with varying degrees of oxygen
incorporation, but only films deposited at a temperature ≥325
°C were continuous. The lowest measured resistivity was 18.6
μΩ cm for films deposited at 325 °C, which is in broad
agreement with the purity and continuity of the films.
Films deposited at a substrate temperature of 300 °C and
below were found to consist of a regular array of cobalt metal
nanoclusters, the size of which appears to be dependent on the
deposition temperature, and is likely to be dependent on the
deposition time also. Those films which were crystalline, show
that the deposited cobalt adopts the fcc crystal structure, as
indicated by PXRD analysis; crystallinity and surface coverage
were found to increase proportionally with increasing
deposition temperature. More significantly, complex 2a
represents a precursor capable of depositing cobalt metal
onto silicon substrates at a low enough temperature to preclude
the concomitant formation of cobalt silicide.
2b (η5-C5H5)Co(η2-tBu2dab). Sublimation (5 × 10−2 mbar, 70 °C)
yielded 1.13 g (77%) of a yellow-brown solid. Analysis. Calc.: C
61.63%, H 8.62%, N 9.58%; Found: C 61.54%, H 8.54%, N 9.46%. 1H
t
NMR (300.22 MHz, C6D6, 298 K) δ: 1.78 (s, 18H, Bu), 4.73 (s, 5H,
η5-Cp), 7.17 (s, 2H, HCN). 13C{1H} NMR (75.50 MHz, C6D6,
298K) δ: 32.8 (CMe3), 64.9 (CMe3), 75.7 (η5-Cp), 134.9 (HCN).
2c (η5-C5H5)Co(η2-Cy2dab). Sublimation (5 × 10−2 mbar, 90 °C)
yielded 1.05 g (61%) of a yellow-brown solid. Analysis. Calc.: C
66.25%, H 8.49%, N 8.13%; Found: C 66.16%, H 8.46%, N 8.12%. 1H
NMR (300.22 MHz, C6D6, 298 K) δ: 1.02−1.22 (m, 4H, CH2), 1.32−
1.51 (m, 4H, CH2), 1.56−1.79 (m, 8H, CH2), 2.39−2.52 (m, 4H,
CH2), 4.63 (s, 5H, η5-Cp), 7.01 (s, 2H, HCN). 13C{1H} NMR
(75.50 MHz, C6D6, 298 K) δ: 25.1 (CH2), 27.0 (CH2), 36.0 (CH2),
73.8 (CH), 76.0 (η5-Cp), 134.4 (HCN).
2d (η5-C5H5)Co(η2-Mes2dab). Recrystallization from a saturated
hexane solution at −28 °C yielded 1.17 g (56%) of a dark brown solid.
Analysis. Calc.: C 72.10%, H 7.02%, N 6.72%; Found: C 72.21%, H
6.93%, N 6.66%. 1H NMR (300.22 MHz, C6D6, 298 K) δ: 2.31 (s, 6H,
p-Me), 2.41 (s, 12H, o-Me), 4.10 (s, 5H, η5-Cp), 6.64 (s, 2H, HC
N,), 6.96 (s, 4H, Mes-CH). 13C{1H} NMR (75.50 MHz, C6D6, 298 K)
δ: 18.6 (o-Me), 21.6 (p-Me), 77.0 (η5-Cp), 129.1 (Mes-CH), 130.3 (o-
C-Me), 134.6 (p-C-Me), 138.5 (HCN), 157.2 (N-C).
2e (η5-C5H5)Co(η2-Dipp2dab). Recrystallization from a saturated
hexane solution at −28 °C yielded 1.43 g (57%) of a dark brown solid.
Analysis. Calc.: C 74.38%, H 8.26%, N 5.57%; Found: C 74.28%, H
Studies into the utility of complexes 2a−c in ALD of cobalt
thin films, at significantly lower temperatures are presently
underway.
1
8.24%, N 5.57%. H NMR (300.22 MHz, C6D6, 298 K) δ: 1.09 (d,
12H, iPr-Me, J = 6.9 Hz), 1.43 (d, 12H, iPr-Me, J = 6.9 Hz), 3.75 (sep,
4H, iPr−CH, J = 6.9 Hz), 4.26 (s, 5H, η5-Cp), 6.79 (s, 2H, HCN),
7.22−7.26 (m, 4H, aryl-CH,), 7.31−7.38 (m, 2H, aryl-CH,). 13C{1H}
NMR (75.50 MHz, C6D6, 298 K) δ: 23.7 (iPr-Me), 26.7 (iPr-Me), 28.7
(iPr-CH), 76.8 (η5-Cp), 123.5 (m-CH), 126.9 (p-CH), 139.6 (HC
N), 141.6 (o-C), 156.5 (C-N).
EXPERIMENTAL SECTION
■
Tristriphenylphosphine cobalt(I) chloride,48 and sodium cyclo-
pentadienide were all made according to literature procedures. N,N′-
di-isopropyldiazabutadiene, N,N′-di-tertbutyldiazabutadiene, N,N′-di-
cyclohexyldiazabutadiene, N,N′-di-mesityldiazabutadiene, and N,N′-di-
(2,6-di-isopropylphenyl)diazabutadiene were made using a modified
general literature procedure.49
Materials Chemistry. TGA Analysis of the complexes was
performed at SAFC Hitech, Bromborough, U.K., using a Shimadzu
TGA-51 Thermogravimetric Analyzer. Data points were collected
every second at a ramp rate of 20 °C min−1 in a flowing (50 mL
min−1) N2 stream. Thin films were deposited using a modified cold-
walled CVD system (Electrogas Systems Ltd., U.K.). The system
consisted of a tubular quartz reactor containing a silicon carbide coated
graphite susceptor. The temperature of the susceptor was monitored
using a k-type thermocouple coupled with a proportional−integral−
derivative controller (PID controller), and heated with a water cooled
IR lamp mounted externally beneath the reaction tube. The pressure
of the system was maintained at 760 Torr throughout the deposition
run, with the reactor lines and precursor, held in a bubbler, at 130 °C.
The vapor generated was delivered to the reaction zone using a high
purity hydrogen (99.998%) carrier gas (300 mL/min) metered from a
mass flow controller. Films were deposited onto CVD coated
ruthenium on silicon wafers at a susceptor temperature of between
250 and 300 °C. The total deposition time was 30 min.
General Procedures. Elemental analyses were performed by
Elemental Analysis Service, SASC, London Metropolitan University,
1
London, U.K. H and 13C NMR spectra were recorded on a Bruker
Avance 300 MHz FT−NMR spectrometer; chemical shifts are quoted
in units of ppm, relative to Me4Si (1H, 13C); coupling constants are in
hertz (Hz).
All reactions were carried out under an inert atmosphere, and in the
absence of light, using standard Schlenk techniques. Solvents were
dried over activated alumina columns using an Innovative Technology
solvent purification system (SPS) and degassed under an argon
atmosphere. All other reagents were purchased from commercial
sources.
Synthesis of 2a−e. 2a (η5-C5H5)Co(η2-iPr2dab). A 2 M solution of
sodium cyclopentadienyl in tetrahydrofuran (THF, 2.5 mL, 5 mmol)
was added to a solution of tris(triphenylphosphine) cobalt(I) chloride
(4.41 g, 5 mmol) in THF (30 mL) at −78 °C. The solution was
allowed to warm to room temperature over a period of 1 h and was
stirred for an additional hour. N,N′-Di-isopropyldiazabutadiene (0.70
Raman spectroscopy was recorded on a Renishaw InVia Raman
using a 532 nm (green) laser. XPS measurements were performed on a
I
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Kratos Axis Ultra-DLD photoelectron spectrometer, utilizing mono-
chromatic Al Kα radiation (photon energy 1486.6 eV), at the
University of Cardiff. The instrument was precalibrated using pure
gold and copper samples. Samples were sputtered for a predetermined
set time over a 4 mm wide area using 4 kV argon ions using a
minibeam I ion source. Spectra were collected at pass energies of 80
and 160 eV for high resolution and survey scans respectively, with the
100 μm apperture in place to focus on the center of the etch pit. FE-
SEM analysis of the films was undertaken on a JEOL JSM-6480LV
scanning electron microscope with EDX capability. TEM analysis was
undertaken on a JEOL 1200EX, using nickel grids, at the University of
Bath. AFM analysis was performed using a Digital Instruments
Nanoscope IIIa, with TAP300 tips in contact mode (Tip radius <10
nm). Powder XRD of the films was performed on a Bruker D8 Powder
Diffractometer, using a Cu anode X-ray source, (Kα wavelength =
1.5406 Å) at the University of Bath. Sheet resistivity measurements
were recorded using a Jandel Multiheight 4-point probe in
combination with a Guardian Surface Resistivity Meter Model
#SRM-232-100, with a sheet resistance range of 0−100 ohm/sq.
Crystallography. Experimental details relating to the single-crystal
X-ray crystallographic studies are summarized in Table 2. For both
structures, data were collected on a Nonius Kappa CCD diffractometer
at 150(2) K using Mo−Kα radiation (λ = 0.71073 Å). Structure
solution and refinements were performed using SHELX8650 and
SHELX9751 software, respectively. Corrections for absorption were
made in all cases. Data were processed using the Nonius Software.52
Structure solution, followed by full-matrix least-squares refinement was
performed using the WINGX-1.80 suite of programs throughout.53
For all complexes, hydrogen atoms were included at calculated
positions. Data for complexes 2c and 2d are deposited with the
Cambridge Structural Database with CCDC reference numbers
956829−956830.
(4) Gay, J. G.; Richter, R. In Ultrathin Magnetic Structures; Bland, J. A.
C., Heinrich, B., Eds.; Springer: Berlin, Germany, 1994; p 21.
(5) Lee, H.-B.-R.; Kim, H. J. Cryst. Growth 2010, 312, 2215.
(6) (a) Londergan, A. R.; Nuesca, G.; Goldberg, C.; Peterson, G.;
Kaloyeros, A. E.; Arkles, B.; Sullivan, J. J. J. Electrochem. Soc. 2001, 148,
C21. (b) Kutschera, M.; Groth, T.; Kentsch, C.; Shumay, I. L.;
Weinelt, M.; Fauster, T. J. Phys.: Condens. Matter 2009, 21. (c) Gross,
M. E.; Kranz, K. S.; Brasen, D.; Luftman, H. J. Vac. Sci. Technol. B
1988, 6, 1548. (d) Rhee, H. S.; Ahn, B. T.; Sohn, D. K. J. Appl. Phys.
1999, 86, 3452. (e) Rhee, H. S.; Ahn, B. T. J. Electrochem. Soc. 1999,
146, 2720. (f) Rhee, H. S.; Ahn, B. T. Appl. Phys. Lett. 1999, 74, 3176.
(g) Rhee, H. S.; Jang, T. W.; Ahn, B. T. Appl. Phys. Lett. 1999, 74,
1003. (h) Rhee, H. S.; Sohn, D. K.; Ahn, B. T. Mater. Res. Soc., Symp.
Proc. 1999, 564, 145.
(7) (a) Henderson, L. B.; Ekerdt, J. G. Microelectron. Eng. 2010, 87,
588. (b) Khan, R. A.; Bhatti, A. S. J. Magn. Magn. Mater. 2010, 323,
340. (c) Olivier, S.; Decorps, T.; Calvo-Munoz, M.-L.; Da Silva, S.;
Cayron, C.; Haumesser, P.-H.; Passemard, G. Thin Solid Films 2010,
518, 4773. (d) Zhang, L.; Ho, P. S.; Aubel, O.; Hennesthal, C.;
Zschech, E. J. Mater. Res. 2011, 26, 2757. (e) Yang, C. C.; Flaitz, P.; Li,
B.; Chen, F.; Christiansen, C.; Lee, S. Y.; Ma, P.; Edelstein, D.
Microelectron. Eng. 2012, 92, 79. (f) Yang, C. C.; Baumann, F.; Wang,
P. C.; Lee, S. Y.; Ma, P.; AuBuchon, J.; Edelstein, D. Microelectron. Eng.
2013, 106, 214.
(8) Cobo, S.; Heidkamp, J.; Jacques, P. A.; Fize, J.; Fourmond, V.;
Guetaz, L.; Jousselme, B.; Ivanova, V.; Dau, H.; Palacin, S.; Fontecave,
M.; Artero, V. Nat. Mater. 2012, 11, 802.
(9) (a) Ohzuku, T.; Ueda, A. Solid State Ionics 1994, 69, 201.
(b) Ritchie, A. G. J. Power Sources 2004, 136, 285. (c) Wu, H. B.;
Chen, J. S.; Hng, H. H.; Lou, X. W. Nanoscale 2012, 4, 2526. (d) Woo,
J. H.; Trevey, J. E.; Cavanagh, A. S.; Choi, Y. S.; Kim, S. C.; George, S.
M.; Oh, K. H.; Lee, S.-H. J. Electrochem. Soc. 2012, 159, A1120.
(e) Scott, I. D.; Jung, Y. S.; Cavanagh, A. S.; Yan, Y.; Dillon, A. C.;
George, S. M.; Lee, S.-H. Nano Lett. 2011, 11, 414. (f) Jung, Y. S.;
Cavanagh, A. S.; Gedvilas, L.; Widjonarko, N. E.; Scott, I. D.; Lee, S.-
H.; Kim, G.-H.; George, S. M.; Dillon, A. C. Adv. Energy Mater. 2012,
2, 1022. (g) Donders, M. E.; Arnoldbik, W. M.; Knoops, H. C. M.;
Kessels, W. M. M.; Notten, P. H. L. J. Electrochem. Soc. 2013, 160,
A3066.
ASSOCIATED CONTENT
* Supporting Information
■
S
XPS spectra of the films deposited at 250 °C, 275 °C, 300 °C,
325 °C, and 350 °C are provided. X-ray crystallographic files in
CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
(10) (a) Thurn-Albrecht, T.; Schotter, J.; Kastle, C. A.; Emley, N.;
Shibauchi, T.; Krusin-Elbaum, L.; Guarini, K.; Black, C. T.; Tuominen,
M. T.; Russell, T. P. Science 2000, 290, 2126. (b) Sellmyer, D. J.;
Zheng, M.; Skomski, R. J. Phys.: Condens. Matter 2001, 13, R433.
(c) Zhang, J.; Lima, F. H. B.; Shao, M. H.; Sasaki, K.; Wang, J. X.;
Hanson, J.; Adzic, R. R. J. Phys. Chem. B 2005, 109, 22701.
(11) (a) Cheng, J. Y.; Ross, C. A.; Chan, V. Z. H.; Thomas, E. L.;
Lammertink, R. G. H.; Vancso, G. J. Adv. Mater. 2001, 13, 1174.
(b) New, R. M. H.; Pease, R. F. W.; White, R. L. J. Vac. Sci. Technol., B
1994, 12, 3196. (c) Ko, Y. K.; Park, D. S.; Seo, B. S.; Yang, H. J.; Shin,
H. J.; Kim, J. Y.; Lee, J. H.; Lee, W. H.; Reucroft, P. J.; Lee, J. G. Mater.
Chem. Phys. 2003, 80, 560.
(12) (a) Alameda, J. M.; Carmona, F.; Salas, F. H.; AlvarezPrado, L.
M.; Morales, R.; Perez, G. T. J. Magn. Magn. Mater. 1996, 154, 249.
(b) Sarkar, A.; Adhikari, R.; Das, A. K. Phys. B 2012, 407, 4148.
(13) (a) Boyd, E. P.; Ketchum, D. R.; Deng, H.; Shore, S. G. Chem.
Mater. 1997, 9, 1154. (b) Charles, R. G.; Haverlac., Pg J. Inorg. Nucl.
Chem. 1969, 31, 995. (c) Chioncel, M. F.; Haycock, P. W. Chem. Vap.
Deposition 2005, 11, 235. (d) Dormans, G. J. M.; Meekes, G. J. B. M.;
Staring, E. G. J. J. Cryst. Growth 1991, 114, 364. (e) Lane, P. A.; Oliver,
P. E.; Wright, P. J.; Reeves, C. L.; Pitt, A. D.; Cockayne, B. Chem. Vap.
Deposition 1998, 4, 183. (f) Lee, J.; Lee, J. G. J. Korean Phys. Soc. 2006,
49, S697. (g) Lee, J.; Park, H.; Lee, J. Diffus. Defect Data, Pt. B 2007,
124−126, 531. (h) Lee, K.; Park, T.; Lee, J.; Kim, J.; Kim, J.; Kwak, N.;
Yeom, S.; Jeon, H. Jpn. J. Appl. Phys. 2008, 47, 5396. (i) Maruyama, T.
Jpn. J. Appl. Phys. 1997, 36, L705. (j) Mordi, C. U.; Eleruja, M. A.;
Taleatu, B. A.; Egharevba, G. O.; Adedeji, A. V.; Akinwunmi, O. O.;
Olofinjana, B.; Jeynes, C.; Ajayi, E. O. B. J. Mater. Sci. Technol. 2009,
25, 85. (k) Papadopoulos, N.; Karayianni, C.-S.; Tsakiridis, P.;
Sarantopoulou, E.; Hristoforou, E. Chem. Vap. Deposition 2011, 17,
AUTHOR INFORMATION
Corresponding Author
*E-mail: A.L.Johnson@bath.ac.uk. Phone: 44 (0)1225 384467.
Fax: 44 (0)1225 386231.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge the financial support of the University of Bath
(studentships to T.P.) and SAFC-Hitech for case-award
support (T.P.).
REFERENCES
■
(1) Kodas, T. T., Hampden-Smith, M. J., Eds.; The chemistry of metal
CVD; VCH: Weinheim, Germany, 1994.
(2) (a) Pratt, W. P.; Lee, S. F.; Holody, P.; Yang, Q.; Loloee, R.; Bass,
J.; Schroeder, P. A. J. Magn., Magn. Mater. 1993, 126, 406. (b) Pratt,
W. P.; Lee, S. F.; Yang, Q.; Holody, P.; Loloee, R.; Schroeder, P. A.;
Bass, J. J. Appl. Phys. 1993, 73, 5326.
(3) (a) Balke, B.; Wurmehl, S.; Fecher, G. H.; Felser, C.; Kubler, J.
Sci. Technol. Adv. Mater. 2008, 9. (b) Ernult, F.; Yakushiji, K.; Mitani,
S.; Takanashi, K. J. Phys.: Condens. Matter 2007, 19. (c) Tsymbal, E. Y.;
Belashchenko, K. D.; Velev, J. P.; Jaswal, S. S.; van Schilfgaarde, M.;
Oleynik, I. I.; Stewart, D. A. Prog. Mater. Sci. 2007, 52, 401.
(d) Yakushiji, K.; Mitani, S.; Ernult, F.; Takanashi, K.; Fujimori, H.
Phys. Rep. 2007, 451, 1.
J
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
211. (l) Papadopoulos, N. D.; Illekova, E.; Karayanni, H. S.;
Hristoforou, E. J. Optoelectron. Adv. Mater. 2008, 10, 1098. (m) Ye,
D. X.; Pimanpang, S.; Jezewski, C.; Tang, F.; Senkevich, J. J.; Wang, G.
C.; Lu, T. M. Thin Solid Films 2005, 485, 95.
(14) Ivanova, A. R.; Nuesca, G.; Chen, X. M.; Goldberg, C.;
Kaloyeros, A. E.; Arkles, B.; Sullivan, J. J. J. Electrochem. Soc. 1999, 146,
2139.
(15) West, G. A.; Beeson, K. W. Appl. Phys. Lett. 1988, 53, 740.
(16) Choi, H.; Park, S. Chem. Mater. 2003, 15, 3121.
(17) Bandoli, G.; Barreca, D.; Gasparotto, A.; Maccato, C.; Seraglia,
R.; Tondello, E.; Devi, A.; Fischer, R. A.; Winter, M. Inorg. Chem.
2009, 48, 82.
(18) Odedra, R.; Boag, N.; Anthis, J.; Kanjolia, R.; (Sigma-Aldrich
Co., U.S.A.). Patent Application: WO 2011017068, 2011.
(19) Kim, K.; Lee, K.; Han, S.; Jeong, W.; Jeon, H. J. Electrochem. Soc.
2007, 154, H177.
(35) Rosa, V.; Gonzalez, P. J.; Aviles, T.; Gomes, P. T.; Welter, R.;
Rizzi, A. C.; Passeggi, M. C. G.; Brondino, C. D. Eur. J. Inorg. Chem.
2006, 4761.
(36) Tanabiki, M.; Sunada, Y.; Nagashima, H. Organometallics 2007,
26, 6055.
(37) Rosa, V.; Carabineiro, S. A.; Aviles, T.; Gomes, P. T.; Welter, R.;
Campos, J. M.; Ribeiro, M. R. J. Organomet. Chem. 2008, 693, 769.
(38) Khusniyarov, M. M.; Harms, K.; Burghaus, O.; Sundermeyer, J.
Eur. J. Inorg. Chem. 2006, 2985.
(39) Sieger, M.; Hubler, K.; Scheiring, T.; Sixt, T.; Zalis, S.; Kaim, W.
Z. Anorg. Allg. Chem. 2002, 628, 2360.
(40) Pronin, I. I.; Valdaitsev, D. A.; Voronchikhin, A. S.;
Gomoyunova, M. V.; Contri, S. F.; Benedetti, S.; Lukes, P.; Valeri,
S. Tech. Phys. Lett. 2005, 31, 494.
(41) Paranjape, M. A.; Mane, A. U.; Raychaudhuri, A. K.; Shalini, K.;
Shivashankar, S. A.; Chakravarty, B. R. Thin Solid Films 2002, 413, 8.
(42) (a) Aprilesi, G.; Mazzega, E.; Michelini, M.; Nava, F.; Queirolo,
G.; Meda, L. J. Appl. Phys. 1986, 60, 310. (b) Gruyters, M. Surf. Sci.
2002, 515, 53. (c) Wiemer, C.; Tallarida, G.; Bonera, E.; Ricci, E.;
Fanciulli, M.; Mastracchio, G. F.; Pavia, G.; Marangon, S. Microelectron.
Eng. 2003, 70, 233. (d) Pan, J. S.; Liu, R. S.; Zhang, Z.; Poon, S. W.;
Ong, W. J.; Tok, E. S. Surf. Sci. 2006, 600, 1308.
(43) Liu, F. M.; Ye, J. H.; Ren, B.; Yang, Z. L.; Liao, Y. Y.; See, A.;
Chan, L.; Tian, Z. Q. Thin Solid Films 2005, 471, 257.
(44) Owen, E. A.; Jones, D. M. Proc. Phys. Soc., London B 1954, 67,
456.
(45) Geller, S. Acta Crystallogr. 1955, 8, 83.
(46) Cheng, F. X.; Jiang, C. H.; Wu, J. S. Mater. Trans. 2004, 45,
2471.
(47) Li, Y. J.; Seidel, P.; Machalett, F.; Linzen, S.; Schmidl, F. J. Mater.
Res. 1997, 12, 2072.
(48) Wakatsuki, Y.; Yamazaki, H. Inorg. Synth. 1989, 26, 189.
(49) O’Reilly, R. K.; Shaver, M. P.; Gibson, V. C.; White, A. J. P.
Macromolecules 2007, 40, 7441.
(20) Lee, H.-B.-R.; Kim, H. Electrochem. Solid State Lett. 2006, 9,
G323.
(21) (a) Lee, H.-B.-R.; Park, Y. J.; Baik, S.; Kim, H. Chem. Vap.
Deposition 2012, 18, 41. (b) Diskus, M.; Nilsen, O.; Fjellvag, H. Chem.
Vap. Deposition 2011, 17, 135. (c) Lee, H.-B.-R.; Kim, H. Electrochem.
Solid State Trans. 2008, 16, 219.
(22) Kwon, J.; Saly, M.; Halls, M. D.; Kanjolia, R. K.; Chabal, Y. J.
Chem. Mater. 2012, 24, 1025.
(23) (a) Li, Z.; Lee, D. K.; Coulter, M.; Rodriguez, L. N. J.; Gordon,
R. G. Dalton Trans. 2008, 2592. (b) Lim, B. S.; Rahtu, A.; Park, J.-S.;
Gordon, R. G. Inorg. Chem. 2003, 42, 7951. (c) Wu, J.; Li, J.; Zhou, C.;
Lei, X.; Gaffney, T.; Norman, J. A. T.; Li, Z.; Gordon, R.; Cheng, H.
Organometallics 2007, 26, 2803. (d) Lim Booyong, S.; Rahtu, A.;
Gordon Roy, G. Nat. Mater. 2003, 2, 749. (e) Kim, H. Microelectron.
Eng. 2013, 106, 69.
(24) Knisley, T. J.; Saly, M. J.; Heeg, M. J.; Roberts, J. L.; Winter, C.
H. Organometallics 2011, 30, 5010.
(25) (a) Donders, M. E.; Knoops, H. C. M.; van, M. C. M.; Kessels,
W. M. M.; Notten, P. H. L. J. Electrochem. Soc. 2011, 158, G92.
(b) Han, B.; Choi, K. H.; Park, J. M.; Park, J. W.; Jung, J.; Lee, W.-J. J.
Vac. Sci. Technol. A 2013, 31, 01A145/1. (c) Klepper, K. B.; Nilsen, O.;
Fjellvag, H. J. Cryst. Growth 2007, 307, 457. (d) Klepper, K. B.; Nilsen,
O.; Fjellvag, H. Thin Solid Films 2007, 515, 7772.
(50) Sheldrick, G. M. SHELX-86, Computer Program for Crystal
Structure Determination; University of Gottingen: Gottingen, Germany,
̈
̈
1986.
(51) (a) Sheldrick, G. M. SHELX-97, Computer Program for Crystal
Structure Refinement; Univerity of Gottingen: Gottingen, Germany,
̈
̈
1997; (b) Sheldrick, G. M. Acta Crystallogr. Sect. A 2008, 64, 112.
(52) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology; Carter, C.
W., Jr., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276,
Macromolecular Crystallography, part A, pp 307−326.
(26) Dieck, H. T.; Haarich, M. J. Organomet. Chem. 1985, 291, 71.
(27) Sgro, M. J.; Stephan, D. W. Dalton Trans. 2010, 39, 5786.
(28) (a) Adams, R. D. J. Am. Chem. Soc. 1980, 102, 7476. (b) Zoet,
R.; Vankoten, G.; Stufkens, D. J.; Vrieze, K.; Stam, C. H.
Organometallics 1988, 7, 2118. (c) Zoet, R.; Jastrzebski, J. T. B. H.;
Vankoten, G.; Mahabiersing, T.; Vrieze, K.; Heijdenrijk, D.; Stam, C.
H. Organometallics 1988, 7, 2108. (d) Zoet, R.; Vankoten, G.; Muller,
F.; Vrieze, K.; Vanwijnkoop, M.; Goubitz, K.; Vanhalen, C. J. G.; Stam,
C. H. Inorg. Chim. Acta 1988, 149, 193. (e) Staal, L. H.; Vankoten, G.;
Vrieze, K.; Vansanten, B.; Stam, C. H. Inorg. Chem. 1981, 20, 3598.
(f) Staal, L. H.; Keijsper, J.; Polm, L. H.; Vrieze, K. J. Organomet. Chem.
1981, 204, 101. (g) Staal, L. H.; Vankoten, G.; Vrieze, K.; Ploeger, F.;
Stam, C. H. Inorg. Chem. 1981, 20, 1830. (h) Staal, L. H.; Vankoten,
G.; Vrieze, K. J. Organomet. Chem. 1981, 206, 99. (i) Staal, L. H.;
Keijsper, J.; Vankoten, G.; Vrieze, K.; Cras, J. A.; Bosman, W. P. Inorg.
Chem. 1981, 20, 555.
(53) Farrugia, L. J. J. Appl. Crystallogr. 2012, 45, 849.
NOTE ADDED AFTER ASAP PUBLICATION
■
This paper was published on the Web on November 15, 2013,
with minor text errors in the Abstract. The corrected version
was reposted on November 19, 2013.
(29) Greulich, S.; Kaim, W.; Strange, A. F.; Stoll, H.; Fiedler, J.; Zalis,
S. Inorg. Chem. 1996, 35, 3998.
(30) (a) Overbosch, P.; Vankoten, G.; Overbeek, O. Inorg. Chem.
1982, 21, 2373. (b) Overbosch, P.; Vankoten, G.; Spek, A. L.;
Roelofsen, G.; Duisenberg, A. J. M. Inorg. Chem. 1982, 21, 3908.
(31) Lenges, C. P.; White, P. S.; Marshall, W. J.; Brookhart, M.
Organometallics 2000, 19, 1247.
(32) Ni, C. B.; Stich, T. A.; Long, G. J.; Power, P. P. Chem. Commun.
2010, 46, 4466.
(33) Barral, M. C.; Delgado, E.; Gutierrezpuebla, E.; Jimenezaparicio,
R.; Monge, A.; Delpino, C.; Santos, A. Inorg. Chim. Acta 1983, 74, 101.
(34) Laine, T. V.; Klinga, M.; Maaninen, A.; Aitola, E.; Leskela, M.
Acta Chem. Scand. 1999, 53, 968.
K
dx.doi.org/10.1021/ic402317g | Inorg. Chem. XXXX, XXX, XXX−XXX